Over deze norm

Status

Ontwerp

Aantal pagina's

26

Commissie

Nanotechnologie

Gepubliceerd op

17-05-2016

Taal

Engels

This part of ISO 21501 describes a calibration and verification method for a light scattering airborne particle counter (LSAPC), which is used to measure the size distribution and particle number concentration of particles suspended in air. The light scattering method described in this part of ISO 21501 is based on single particle measurements. The typical size range of particles measured by this method is between 0.1 μm and 10 μm in particle size. Instruments that conform to this part of ISO 21501 are used for the classification of air cleanliness in cleanrooms and associated controlled environments in accordance with ISO 14644-1 and ISO 14644-2, as well as the measurement of number and size distribution of particles in various environments. The following parameters are within the scope of this part of ISO 21501: - size setting; - counting efficiency; - size resolution; - false count; - maximum particle number concentration; - sampling flow rate; - sampling time; - response rate; - calibration Interval. Principle The measurement principle of the LSAPC is based on detection of light scattered by a particle when the particle passes through an incident light beam. The particle size is determined from the intensity of the scattered light, and the number of particles from the number of light pulses scattered by individual particles. To be more specific, sample air is drawn from the inlet of the LSAPC at a constant flow rate, and introduced to the sensing volume of the LSAPC where a light beam is irradiated. When a particle suspended in the sample air passes through the light beam, it scatters the light, emitting a light pulse. The light pulse is detected by a photo detector, and converted to an electrical pulse. The electrical pulse height is proportional to the scattered light intensity, and depends on the optical system design, the electronic components used, and the light source. The intensity of the scattered light is dependent on the size, refractive index, and shape of the particle. If the particle is spherical, the scattered light intensity is described by the Mie theory. In order to establish a relationship between the electrical pulse height and the particle size, calibration of each LSAPC with use of particles having a well-defined size, refractive index, and shape is required.